(PHP Extension) Convert RSA Private Key to Public Key

Demonstrates how to get a public RSA key from a private RSA key.

Chilkat PHP Downloads PHP Extension for Windows, Linux, MacOS, Alpine Linux, Solaris

<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

$key = new CkPrivateKey();

// Step 1: Load the private key from a source.
// (Chilkat can load private keys from all types of formats, and from in-memory bytes or encoded strings.
// see the online reference documentation for more options.)
$success = $key->LoadPemFile('qa_data/pem/VP_Private.pem');
if ($success != true) {
    print $key->lastErrorText() . "\n";
    exit;
}

// Step 2: Get the public key object from the private key object.
// pubKey is a CkPublicKey
$pubKey = $key->GetPublicKey();
if ($key->get_LastMethodSuccess() != true) {
    print $key->lastErrorText() . "\n";
    exit;
}

// Step 3: Save the public key in a desired format. 
// (Chilkat can load or save public and private keys in many different formats.  See
// the online reference documentation for more options.)

// Saves to a PKCS8 PEM file.
$bPreferPkcs1 = false;
$success = $pubKey->SavePemFile($bPreferPkcs1,'qa_data/pem/VP_Public.pem');
if ($pubKey->get_LastMethodSuccess() != true) {
    print $pubKey->lastErrorText() . "\n";
    exit;
}

print 'Extracted and saved public key from private key.' . "\n";

?>